The invention relates to a power unit bearing, in principle for arbitrary purposes, in specific however for motor vehicles.
Power unit bearings or so-called xe2x80x9cengine mountsxe2x80x9d support a motor-vehicle power unit on the chassis. Such bearings are intended to elastically absorb assembly vibrations, to dampen them and in particular to decouple them acoustically and sub-acoustically. Bearings of the most diverse designs meet these tasks in significantly different ways. Rubber-metal bearings of most varied designs with, as well as without, hydraulic damping have been found foremost practical.
As hardly any one bearing meets the broad requirements of vehicle comfort, innumerable bearings already have become known with the purpose of controlling or setting or modifying the bearing characteristics. In the field of solid bearings, that is foremost the field of rubber-metal bearings, the elastic rubber body is contoured to hopefully match a particular desired spring constant. As regards hydraulic bearings, that is bearings with a hydraulic damping liquid, foremost those bearings are known in which electrical or magnetic fields control the rheological properties of the damping liquid.
The effectiveness of all known bearings is limited in that the known means and procedures to control the bearing characteristics of power unit bearings are able to respond to only comparatively narrow and homogeneous ranges and bands of frequencies and amplitudes. Bearings are not known which for instance are able to both insulate such vibrations illustratively caused by an idling engine at low rpm and to decouple and dampen such vibrations that are generated caused by an engine running at a higher rpm in a moving vehicle, are not known.
In the light of this general state of the art, it is the objective of the present invention to create power unit bearings and in particular a motor-vehicle bearing which shall be able both to decouple and dampen low-frequency vibrations of large amplitudes such as are generated typically by an idling engine and vibrations of higher and high frequencies of small amplitudes that are generated by the drive assembly at higher rpms and vehicles moving at significant speeds.
Accordingly the basic concept of the invention is not in matching a power unit bearing known per se to its most diverse operating conditions by additionally modifying the bearing itself in complex manner and by acting in increasingly effective manner on the inherent bearing properties, but in that the actual, conventional and well-tested bearing itself is mounted on a switching module and in fact is integrated together with this switching module into one subassembly of which the specific bearing properties can be added to or decoupled from those of the conventional bearing. If the switching module is engaged, the characteristics of the conventional bearing therefore are modified by those of the switching module, whereas when the switching module is disengaged or deactivated, the conventional bearing, ie the bearing body, will be directly and at once transmitted to the chassis adapter of the power unit bearing. In its disengaged state, the switching module""s transmission characteristics are in the ideal case absolutely neutral.
However in practice such a completely transmission-neutral behavior can be implemented in general only at great cost and moreover it is frequently less than mandatorily desirable in view of the acoustics. For that reason the overall structure of the power unit bearing with disengaged switching module preferably shall have a transmission behavior which can be considered being xe2x80x9cextensively neutrally rubber-dampedxe2x80x9d.
The power unit bearing with switching module of the invention can be used both with conventional solid bearings, in particular rubber metal bearings, and with complex hydraulic bearings. Preferably the switching module shall be integral with the actual, conventional bearing body to form a new, integral power unit bearing. The switching module preferably shall be related to the bearing function by means of, and together with, the bearing housing of the conventional bearing portion.
In principle such a switching module can be controlled both mechanically and electrically, electromagnetically or optionally pneumatically and in adjustable manner. Preferably and in particular when used for automotive purposes, the power unit bearing of the invention however shall be switched pneumatically and in the process will behave in its engaged or activated state in the manner of a hydraulic bearing. As a result, and even with simple designs, remarkable effective results are reached, provided that the switching module be fitted with a hydraulic operating chamber in such manner that when the operational fluid in the closed operational chamber is unpressurized, the module shall be disengaged whereas, and also in the closed system, it shall be pressurized in the engaged, activated state of the switching module. In particular hydraulic, axially effective spacing enlargements can be implemented in this manner to separate the previously axially and radially affixed switching module from the conventional bearing body.
It is clear per se that the switching module of the power unit bearing is preferably integrated on the bearing""s chassis side but that kinematically reversed solutions are easily implemented as well whereby the switching module is inserted between the support piece of the bearing and the support spring of the conventional bearing body.
Moreover the switching module even in its hydraulic mode can be designed in further manner in the spring zone using other support means, for instance using an additional rubber spring or steel spring, in particular a spiral compression spring. However the determinant function of the switching module always shall be that in its disengaged state it will allow the characteristics of the conventional bearing body to be operationally as free as possible of spurious effects and that in its activated state it shall support the conventional bearing body so softly, so floatingly and so three-dimensionally that even low-frequency vibrations of high amplitudesxe2x80x94as are generated by a power unit running in idlexe2x80x94shall be decoupled as fully as possible and shall be extinguished.
The invention is elucidated below in relation to an illustrative embodiment.